Numerous methods have been utilized heretofore for tuning musical instruments. These methods have been applied both to the intent of standardizing the basic pitch relationship and also to the more important purpose of establishing the correct pitch relationships between the various notes available from a given musical instrument. Methods have progressed from the definement by ear through the reliance upon the stability of certain musical instruments and musical instrument related devices, such as tuning forks, tuning bars, and the like. Such methods have produced accuracy to a few tenths of a percent, when used by experts.
With the appearance of the digital counter, and direct digital display methods for providing a display therefore, it has become possible to count audio frequencies and far higher frequencies of electrical, single frequency component signals to several parts per million accuracy, utilizing quartz crystal time bases, and to five or six orders of magnitude greater accuracy, using more sophisticated time bases. Measuring musical pitches to a high degree of accuracy has remained a difficult task, because of the complex nature of musical sounds, the fact that sounds produced by musical instruments contain not only a fundamental pitch, but overtones which may range from within an octave to many octaves above the fundamental frequency.
It is the intent of this invention to establish a means of utilizing the presently available technology of digital counters and accurate time bases to provide a means of measuring the pitch of musical sounds to a degree of accuracy approaching the basic accuracy of these devices. In order to accomplish these ends it is necessary to provide a means of measuring the frequency of the fundamental, or predominating component, while rejecting all other harmonically related frequencies in an electrical wave derived from the output of a musical instrument.
The present invention is therefore intended to:
(1) RESPOND TO ONE FREQUENCY OF A CONTINUING SIGNAL, WHILE REJECTING ANY NUMBER OF HARMONICALLY RELATED FREQUENCIES WHICH MAY BE PRESENT WITHIN THAT SIGNAL;
(2) CHECK, CYCLE TO CYCLE, AND ALLOW PRESENTATION OF A DERIVED COUNT OF CYCLES FOR A COUNT PERIOD IF, AND ONLY IF, THE COUNTED WAVE MATCHES THE FREQUENCY OF THE PREDOMINANT COMPONENT OF THE PRESENTED MUSICAL TONE TO A PHASE VARIATION OF PLUS OR MINUS APPROXIMATELY 90 DEGREES;
(3) PROVIDE A MEANS OF COORDINATING AN ACCURATE TIME BASE TO COUNT A SIGNAL FOR AN EXACT PERIOD OF TIME AND DISPLAY THAT COUNT WHILE THE SUCCESSIVE COUNT IS BEING TAKEN, AND AS STATED ABOVE, REFUSE TO DISPLAY A COUNT, INDICATING ZERO, IF A SINGLE FLAW, REPRESENTED BY A SINGLE DEPARTURE OF MORE THAN APPROXIMATELY 90 DEGREES, APPEARING AT ANY TIME BETWEEN THE PREDOMINANT FREQUENCY OF THE MUSICAL NOTE AND THE COMPONENT BEING COUNTED SHOULD OCCUR;
(4) PROVIDE A MEANS OF CONVERTING THE OUTPUT OF A MUSICAL INSTRUMENT TO A USEFUL FORM FOR THE ABOVE PROCESSING;
(5) PROVIDE A USABLE VISIBLE DISPLAY OF A CYCLE COUNT PER TIME PERIOD IN A USABLE LANGUAGE SUCH AS CYCLES PER SECOND; AND
(6) INCLUDE ANY OR ALL OF THE ABOVE MENTIONED FUNCTIONS INTO A PRACTICAL PACKAGE, CONVENIENT TO USE, WHICH WILL ACCOMPLISH THE ABOVE DESCRIBED MISSION.